Was HE consistently removing a measured amount of air?
Speculation:
Measuring the air would not be necessary. Letting the air out for, say, a slow 2-count every time would be sufficient.
One can let the air out of the balls faster by doing two or three at a time. You remove the needles in the same order you inderted them. Needle in to Ball 1, Ball 2, Ball 3 ... Needle out of Ball 1, Ball 2, Ball 3.
Don't think it was done this way in the bathroom ... but if someone had to do it, it's not implausible. If they truly think someone messed with the balls in some way, I'd think first of a switcheroo of ball bags before I thought an exercise in speed deflation.